Question 1

What causes an MOT emissions failure?

Accepted Answer

The five most common causes are: a failed catalytic converter, a faulty lambda (oxygen) sensor, an EGR valve fault, a DPF blockage on diesel cars, or an engine misfire burning fuel incorrectly. A diagnostic scan pinpoints which system is at fault before any parts are ordered.

Question 2

How long does it take to fix an emissions MOT failure?

Accepted Answer

A lambda sensor swap typically takes 1–2 hours. An EGR clean or replacement is usually a half-day job. Catalytic converter replacement can take 2–4 hours depending on access. DPF regeneration or replacement varies — we'll give you a firm time estimate after the diagnostic.

Question 3

Do I get a free retest after an emissions repair?

Accepted Answer

Yes. If MnF Motors carries out the repair that caused the failure, your retest is free within 10 days of the original MOT — in line with DVSA rules.

Question 4

How much does fixing an MOT emissions failure cost in Romford?

Accepted Answer

Cost depends entirely on the root cause. Lambda sensor replacement is typically £80–£180 fitted. EGR valve cleaning or replacement ranges from £120–£350. A catalytic converter can range from £200–£600+ depending on the vehicle. We price honestly and only after a proper diagnosis — no guesswork, no unnecessary parts.

Question 5

Can I drive my car after it fails its MOT on emissions?

Accepted Answer

If your MOT expired on the day of the test, you can drive straight to a garage for repair. If your MOT is still in date, you can continue to drive it legally until the expiry date — but you should book the repair promptly. We can advise you when you call.